Hi,
I am new to this board. I just bought my third Dual Rectifier and I am amazed by the tonal differences I hear between different Dual Rectifiers. After close inspection, I realized that this one had a very peculiar set of pre-amp tubes in it. So I was wondering what other people do? It seems the Pre-amp tubes give you a lot of control over the tone. Any tips for pre-amp tube sets? I am mostly looking for the early 90th sound. The amps are all early 90th.

More specific:
- what is the difference in tone between an STR 420 and an STR 440.
- it appears that the V5 ECC83 needs to be balanced. Anything special about that? There are sets that just have the same ECC83S balanced pre-amp tubes in every slot. Mine seems to have an interesting mix of RFT, JJ ECC83s and some Chinese tubes.

I bought a few extra now for future usage It seems there is agreement that they sounded better than the STR 440.

V1 tube: I have an RFT in there. Do you know what the difference in sound between EH 12AX7 and Tung Sol or the RFT is? Instead of trying a lot of different 12AX7 I am hoping to get some feedback what already worked out for people.

The EHX 12AX7 has a spiral filament in it which is prone to failure when used in positions with high voltage on the cathode. Those are V3 and V4 on any Rectifier schematic I've ever seen.

I also like the EHX and Tung Sol tubes. I'm also really digging the high gain JJ ECC83s (which is also rebranded as Ruby 12AX7ACZ). They are low noise with gains over 100. Mine are all measured from 110 to 120. The theoretical gain of a 12AX7 is 100, so using them ensures you get maximum signal. I have a Tung Sol in V1 and the JJs in all the rest.

"balanced" tubes for phase inverter use is somewhat controversial. Some say it's necessary, some say it's ok, some say it's marketing hype so that tube dealers can charge more.

What type of tubes make up the "peculiar" preamp tube set? Sounds like the previous owner rolled in some tubes, or dumped in their weird ones before selling it. There are a LOT of great used tubes around, which last quite a bit longer than the current production, so after years of use, they still test as new. The old production also in general are able to tolerate the out of spec cathode follower voltages that are often used. I know some people are down on the Russian Spiral filament designs, but it's a good design, and even the original 12AX7/ECC83 spec had only 180V as the cathode to heater voltage limiting value. MB used to use EHX preamp tubes as the "Russian 2" tubes before the Cathode Follower issue was noticed.

Anyway, hopefully MB will run out of the STR 440s so that they can get something different from Russia, Slovakia, or China. There have been a lot of new and improved tube designs coming out of all the factories,.